Your garden this week: planting celandines and dividing perennials

Celandines

• Although the native celandine, Ranunculus ficaria, is best known for its carpets of yellow blooms, plenty of cultivars offer more unusual flower and leaf colours. These can often be found in nurseries, and can be planted now.

• Look out for Ranunculus ficaria var. aurantiacus, which has amber-coloured flowers; and the white-petalled R. ficaria var. albus, which looks more like a tiny anemone. For double blooms, try 'Double Cream' or the yolky 'Double Bronze'.

• As well as choosing plants with good flowers, try cultivars with unusual leaves. 'Collarette' has marbled green leaves, while 'Brazen Hussy' has chocolate-brown foliage which makes a striking contrast with its double-yellow flowers. Suppliers can be found online at www.rhs.org.uk.

• Plant celandines in a moist, rich border. They will tolerate light and heavy soils but, with both extremes, dig in plenty of garden compost or well-rotted manure. Celandines prefer full sun at this time of year, but a little shade in early summer. They die back, retreating below ground before high summer.

• Grow them with miniature daffodils, grape hyacinths and primulas, such as 'Dawn Ansell' or 'Sue Jervis'.

• Generally, the cultivars don't spread as rapidly as the native yellow celandine. If this is a problem, apply a glyphosate-based weedkiller to the leaves. It is difficult to dig out, as the plants produce a multitude of tiny bulbils.

Dividing perennials

• To keep perennial plants growing vigorously and flowering at their best, they need to be lifted and divided into smaller sections every two or three years. This produces extra plants to fill gaps in borders or swap with friends.

• Dividing summer-flowering plants is best done now. Wait until spring-flowering perennials have flowered to avoid diminishing the display.

• Small, fibrous-rooted plants such as heuchera or epimedium are best lifted and teased apart by hand. Clumps of taller, fibrous-rooted perennials, such as astrantia and hemerocallis, are most easily split using two garden forks: insert these into the crown back-to-back so you can lever the clumps apart. Plants with fleshy roots, such as delphiniums, can be cut with a spade or a sharp knife.

• Aim to produce sections containing three to five shoots.

• Replant the sections in well-prepared soil that has been dug over to incorporate organic matter.

• Make sure the plants are at their original depth, with the shoots above the surface when you finish. Water the plants in and apply a fertiliser to the surrounding soil.

Camellia problems

• Many camellias are now producing a glorious display, but if yours isn't, there is usually a way to put this right. And with any luck, this will lead to better results next spring.

• If the flower buds have fallen off, it is likely that the plant didn't get enough water between last July and September. This is particularly common with plants in containers.

• Look out for water-soaked spots on the leaves. These are known as oedemas and can burst to leave warty or corky patches. This is often caused by the roots taking too much moisture, so only water once the compost or soil starts to feel dry. It may also be necessary to repot camellias in containers, as old, compacted compost can encourage oedema.

• Apply ericaceous fertiliser to plants with yellowing leaves.

• If the leaves have a black coating, it's a sign that a sap-sucking insect is feeding on the plant. Known as sooty mould, it grows on the honeydew excreted by pests such as scale insect. Control pests first, then wipe away with a damp cloth.